Inkjet printers produce images by jetting or ejecting droplets of liquid ink from an inkjet printhead onto a recording substrate (e.g., paper). The printhead typically has a front face with a nozzle opening defined therein, through which liquid ink is ejected as droplets onto the recording substrate.
The front face of an inkjet printhead can become contaminated by wetting or drooling of ink. Such contamination can cause or contribute to partial or complete blocking of the nozzle opening within the front fact of the inkjet printhead, cause under- or over-sized ink droplets to be ejected from the inkjet printhead, alter the intended trajectory of ejected ink droplets onto the recording substrate, and the like, all of which degrade the print quality of inkjet printers.
The front fact of an inkjet printhead is typically coated with a material such as polytetrafluoroethylene (PTFE) (e.g., Teflon®) or perfluoroalkoxy (PFA), to protect it. Current printheads have good initial performance with solid ink, including those commercially available from Xerox Corporation. However, over the operational lifetime, the performance degrades and ink does not readily slide over the printhead front face coatings at typical ink-ejecting temperatures. Rather, the ink tends to adhere and flow along the printhead front face coating, leaving a residual ink film which can partially or completely block the nozzle opening within the front face of the inkjet printhead. FIG. 1 is a photograph of the front face of an inkjet printhead after a printing run showing wetting and contamination of a solid ink over most of the area of the front face surrounding nozzle openings. Thus, oleophobic low adhesion coatings which prevent drooling failure are important to improve robustness and reliability, provide for new market penetration for future solid inks.
Solid inks are those characterized by being solid at room temperature and molten at an elevated temperature at which the molten ink is applied to a substrate. Solid inks generally comprise an ink vehicle, one or more waxes, an optional colorant, and one or more optional additives such as viscosity modifiers, antioxidant, plasticizer, and the like. UV curable inks generally comprise a photoinitiator package, a curable carrier material, an optional colorant, and one or more optional additives such as viscosity modifiers, dispersant, synergist, and the like. UV curable phase change inks, a subset of UV curable inks, may also include a gellant and optionally a curable wax. The term “curable” refers, for example, to the component or combination being polymerizable, that is, a material that may be cured via polymerization, including, for example, free radical routes, and/or in which polymerization is photoinitiated though use of a radiation sensitive photoinitiator. For example, the curable carrier material may be one or more curable monomers or a curable wax.
Contamination of an inkjet printhead front face can be minimized somewhat by adopting purging and/or wiping procedures. However, these procedures can undesirably consume time and/or use excessive amounts of ink, thereby decreasing the useful life of the inkjet printhead. Contamination of an inkjet printhead front face can also be minimized somewhat by providing an oleophobic low adhesion printhead front face coating that does not wet significantly with ink ejected from nozzle openings of the printhead. When heated to temperatures typically encountered during printhead fabrication processes, however, the surface property characteristics of known oleophobic low adhesion printhead front face coatings degrade to the point that they cannot be relied upon to minimize contamination of the inkjet printhead front face. Hence a thermally stable oleophobic low adhesion coating that does not degrade in surface properties upon exposure to high fabrication temperatures is needed for printheads.
Other oleophobic low adhesion printhead front face coatings found to be thermally stable comprise fluorinated polyurethane and are disclosed in U.S. patent application Ser. No. 13/275,255 filed Oct. 17, 2011 and U.S. Patent Publication No. 2012/0044298, which are hereby incorporated by reference in their entirety. These coatings show good surface properties, such as high contact angle/low slide angle, with inks in stacking and ink aging tests even after exposure to high fabrication temperatures. However, these coatings may be expensive to manufacture and implement in printheads. Also the thermal stability of these coatings (as shown by onset of decomposition temperature in Thermal Gravimetric Analysis (TGA) scans) only slightly above printhead fabrication temperatures of 290° C., and may lead to less reliability and robustness of printhead fabrication steps.
As such, there is desired an alternative to the conventional print head face plate coatings that are used that would avoid the problems described above. The advantages of such a coating would be fewer printhead related defects, longer front face life, and reduced manufacturing costs for producing the coating.